如何使用JAXB编组注释为@XmlAttachmentRef的DataHandler？

Question

我正在尝试编组一个DataHandler具有JAXB(2.1.12)字段的对象.对于流媒体支持,DataHandler使用@进行注释XmlAttachmentRef.通过Web服务进行序列化和流式处理(JBoss上的Metro)运行良好,但是使用JAXB进行简单的编组却没有.

这是一个精简的例子:

public class DataHandlerAttachmentSerialization {

    @XmlRootElement
    static class RootObject {
        @XmlElement
        @XmlAttachmentRef // Works without this, but required for streaming 
        DataHandler dataHandler = new DataHandler(
                new com.sun.xml.ws.util.ByteArrayDataSource(
                " ".getBytes(), "application/octet-stream"));
    }

    @Test
    public void test() throws JAXBException {
        JAXBContext context = JAXBContext.newInstance(RootObject.class);
        Marshaller marshaller = context.createMarshaller();
        StringWriter writer = new StringWriter();
        marshaller.marshal(new RootObject(), writer);
        Assert.assertNotNull(writer.toString());
    }
}

运行此测试会产生以下堆栈跟踪:

javax.xml.bind.MarshalException
 - with linked exception:
[com.sun.xml.bind.api.AccessorException: java.lang.NullPointerException]
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:318)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:244)
    at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:96)
    ...
Caused by: com.sun.xml.bind.api.AccessorException: java.lang.NullPointerException
    at com.sun.xml.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:246)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:261)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:335)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsSoleContent(XMLSerializer.java:593)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:320)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:494)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:315)
    ... 25 more
Caused by: com.sun.xml.bind.api.AccessorException: java.lang.NullPointerException
    at com.sun.xml.bind.v2.runtime.reflect.AdaptedAccessor.get(AdaptedAccessor.java:74)
    at com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor$CompositeTransducedAccessorImpl.writeLeafElement(TransducedAccessor.java:250)
    at com.sun.xml.bind.v2.runtime.property.SingleElementLeafProperty.serializeBody(SingleElementLeafProperty.java:98)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:332)
    ... 29 more
Caused by: java.lang.NullPointerException
    at com.sun.xml.bind.v2.runtime.SwaRefAdapter.marshal(SwaRefAdapter.java:80)
    at com.sun.xml.bind.v2.runtime.SwaRefAdapter.marshal(SwaRefAdapter.java:65)
    at com.sun.xml.bind.v2.runtime.reflect.AdaptedAccessor.get(AdaptedAccessor.java:72)
    ... 32 more

在80号线SwaRefAdapter是return am.addSwaRefAttachment(data);和am与分配的AttachmentMarshaller am = XMLSerializer.getInstance().attachmentMarshaller;这么看来attachmentMarshaller是空在这一点上,如果@XmlAttachmentRef存在.

我是否需要以不同的方式设置某些内容,或者以不同的方式使用JAXB API来处理附件？

Answer 1

在JAX-WS环境之外使用JAXB时,JAXB实现应默认将XML文档中的二进制内容内联为base64Binary.

这似乎是JAXB的Metro实现中的一个错误(JDK/JRE中包含的RI).如果您使用另一个JAXB实现,例如EclipseLink JAXB(MOXy),这将正常工作.要使用EclipseLink MOXy,请将eclipselink.jar(此处提供)添加到类路径中,并在以下内容中添加jaxb.properties文件和模型类:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

JAX-WS注册AttachmentMarshallers和AttachmentUnmarshallers来处理JAXB模型中的二进制内容.如果需要,可以在使用JAXB独立时指定自己的.

http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/javax/xml/bind/attachment/AttachmentMarshaller.html